Left 4 Dead 2

Every time I try to play The Passing as soon as it finishes loading the game crashes to the desktop and I get an error message that says: 5/ - survivor_bot: UTIL_SetModel: not precached: models/survivors/survivor_biker.mdlNote that it has done this for every character, not just Francis, anybody know what to do?

Every time I try to play The Passing as soon as it finishes loading the game crashes to the desktop and I get an error message that says: 5/ - survivor_bot: UTIL_SetModel: not precached: models/survivors/survivor_biker.mdlNote that it has done this for every character, not just Francis, anybody know what to do?